A number of procedures exist in a variety of industries which involve the manipulation, counting, and transfer of microscopically-sized particles. Such particles typically may range in size from approximately 0.1 micrometer to 100 micrometers or larger, and may comprise microballoons, microspheres, microbeads, dust, liquid or gas contaminants, or powders used in chemical formulations. The grading or sizing of such particles is a common and widespread industrial process. Furthermore, the counting of such particles is also required in certain test and industrial procedures. For example, it is frequently required to calibrate so-called electronic particle counters of the type used in contamination control studies, blood-cell counting, examination of hydraulic fluid contaminants, etc. The calibration of such counters is conventionally accomplished by introducing a known quantity of suitably-sized microspheres or microbeads into the counter. In other cases, a sample of the particles to be counted or graded is arranged on a microscope slide with a superimposed reticle to permit examination by microscope or by means of an optical comparator. It is found that frequently, electrostatic charges tend to cause the beads or particles to congregate into inseparable clusters on the microscope slide. Furthermore, electrostatic charges on the separating probe tend to cause the beads to disperse in many directions, or to disperse into smaller clusters. Where the particles or beads are introduced into an electronic particle counter, the beads have a tendency to stick to the bottle they are contained in and the counter walls or the conduits through which the beads must pass in the counter, as a result of the buildup of small but significant static charges therein.
The use of ionizing radiation, controlled humidity, and other well-known techniques have been attempted heretofore to suppress troublesome electrostatic charges in the handling of small particles. However, such procedures have not been altogether satisfactory, and in many instances interfere with the intended result.